Prostate cancer (PCa) is a common cancer in men and may cause over 25,000 deaths in the United States alone in 2015. Conventionally, prostate cancer has been diagnosed using a multi-step approach. For example, a biopsy may be performed after a test that revealed worrisome levels of a prostate specific antigen (PSA). In some cases, invasive biopsies may be obtained without a priori knowledge of the location or existence of focal lesions identified on imaging. The biopsy may be performed by transrectal ultrasound (TRUS) guidance, blind to the cancerous lesion or with various forms of targeting with an MRI, and may involve sampling regions of the gland. These multiple steps may have required multiple visits to the hospital over an extended period of time, during which the patient may have been anxious or otherwise inconvenienced. Even after all the steps were taken, a diagnosis may still have been a subjective thing based on how a doctor interpreted the results of the tests for any specific patient. Interpretation may have been subjective with different doctors arriving at different diagnoses. Additionally, excessive biopsy and treatment of low grade PCa may cause more harm than good.
Magnetic resonance (MR) techniques have been employed to attempt to differentiate normal tissue from PCa. For example, conventional T2 weighted images, diffusion weighted images (DWI) with apparent diffusion coefficient (ADC) mapping, dynamic contrast-enhanced MRI (DCE-MRI), and MR spectroscopy (MRS) have been evaluated for differentiating normal tissue from PCa. The ability to use these conventional tools may have been limited by the qualitative nature of the images and the resulting subjective analysis.
When MR images are generated, they may be viewed by a radiologist and/or surgeon who interprets the qualitative images for specific disease signatures. The radiologist may examine multiple image types (e.g., T1-weighted, T2-weighted) acquired in multiple imaging planes to make a diagnosis. The radiologist or other individual examining the qualitative images may need particular skill to be able to assess changes from session to session, from machine to machine, and from machine configuration to machine configuration. Different viewers may arrive at different diagnoses when reading the same images.
Characterizing tissue species using nuclear magnetic resonance (NMR) can include quantifying different properties of a resonant species (e.g., T1 spin-lattice relaxation, T2 spin-spin relaxation, proton density). Other properties like tissue types and super-position of attributes can also be identified using NMR signals. These properties and others may be identified simultaneously using magnetic resonance fingerprinting (MRF), which is described in Magnetic Resonance Fingerprinting, Ma D et al., Nature 2013:495, (7440):187-192. MRF has not previously been applied to identifying or grading PCa.